Conventionally, a group multiple address in a network comprising a center and a plurality of local terminals connected thereto through a single common transmission line such as in an LAN (local area network) or a CATV (community antenna television) is conducted in such a manner that the center sends out data with a group address (representation address) which is predetermined for each group of the local terminals as its transmission destination address, and the local terminal receives the data including the group address of that group to which the terminal belongs.
The operation of the group multiple address will be described with the use of a network shown in FIG. 5:
In FIG. 5, the reference numeral 100 designates a center having a picture data bank, constituted by a device such as a mini-computer, and the picture data is stored in the external memory device thereof. The reference numerals 101 to 105 designate local terminals connected to the center 100 through a single common transmission line 106, which terminals are intended to receive (and decode) the data sent from the center 100 thereby to display the same on a display. Hardware for exclusive use or a personal computer may be used as the local terminal. The local terminals 101 to 105 have terminal addresses of #1 to #5, respectively, and the local terminals 101, 102, and 105 have a group address of #100, the terminal 103 a group address of #101, and the terminal 104 a group address of #102, respectively.
The still picture data is transmitted in a packet form shown in FIG. 6. The packet comprises a header section 201 and a data section 202. The header section 201 includes an address field 204 for containing an address designating a transmission destination, which address is intended to make only the local terminal of that address receive this packet.
The manner of transmission will be described with reference to FIG. 7:
At first in a usual transmission, when the data TXA is transmitted with the transmission destination address #1, only the local terminal of address #1 receives the data TXA (refer to 400 in FIG. 7). Similarly as above when the data TXB, TXC, TXD, TXE are transmitted with the transmission destination address #2, #3, #4, and #5, only the local terminals #2, #3, #4, and #5 receive the data TXB, TXC, TXD, and TXE, respectively (refer to 401 to 404).
Nextly, when the data TXF is transmitted with the group address #100, that data TXF is received by the local terminals #1, #2, and #5 having a group address of #100, realizing a group multiple address (refer to 405). However, in this method, when the multiple address group should be changed, for example, into such that the data TXG should be multiple addressed to the local terminals of #1, #2, #4, and #5, the following operation must be conducted: The data TXG is, at first, sent out to the local terminal #4 (refer to 406), and the data TXG is again sent out with the group address #100, thereby to multiple address the local terminals #1, #2, and #5 (refer to 407).
In the prior art still picture transmission apparatus under such a construction, a group address must be predetermined in conducting a group multiple address, and therefore it was impossible to change the group of the local terminals in the midst of system operation.